1674 DIESEL TRUCK ENGINE Cooling System Caterpillar

Cooling System
1.1. Testing Cooling System Pressure

The engine should be equipped with a radiator which has a sealed pressure radiator cap for pressurizing the cooling system. Pressurizing the cooling system serves two purposes. First, it permits safe operation at coolant temperature higher than the normal boiling point; thereby, providing a margin of cooling for those intermittent peak loads. Secondly, it helps prevent cavitation in the water pump and reduces the possibility of air or steam pockets forming in the coolant passages.

Many times, overheating of the engine is caused by failure to make simple systematic inspections. Visual inspections should be made before instrumentation testing.

COOLANT LEVEL: Check the engine coolant level daily (with engine stopped). Always release cooling system pressure before checking. Fill to the proper level with water free as possible from scale forming minerals, not softened water.

During freezing weather add sufficient permanent type antifreeze to the coolant to prevent freezing.


Add coolant slowly to a hot engine to prevent possible cracking or distorting the cylinder head.

Most commercial antifreeze solutions contain rust inhibitors, however, it is recommended the adding of AVSpare Coolant System Inhibitor to glycol base antifreeze if protection is for temperatures above -20°F (-29°C). If protection is for temperatures -20°F (-29°C) or below, do not add inhibitor. Follow instructions given on the container.

------ WARNING! ------

Inhibitor contains alkali. Avoid contact with eyes. Avoid prolonged or repeated contact with skin.


If a loss of coolant is noticeable, check for leaks in the system. After filling the system, start the engine and recheck the coolant level after normal operating temperature is reached. Running the engine at operating temperature will permit the thermostat to open and allow the coolant to circulate through the entire system and purge air from the engine.

CLEANING THE RADIATOR: Every 10,000 miles clean dirt and trash from between the tubes of the radiator which may cause excessively high operating temperature. Wash, brush or blow the dirt out with whichever method is available and most effective.

CLEANING THE COOLING SYSTEM: Clean the cooling system periodically. Mineral deposits can cause serious engine damage by retarding the transfer of heat to the coolant. A deposit of lime 1/32 inch thick insulates the same amount as 2 inches of steel, reducing the heat transfer substantially. Loose scale and sediment deposited in the cooling system will reduce circulation, resulting in possible engine damage. To clean, stop the engine when it is at normal operating temperature and drain as quickly as possible. Flush thoroughly, then fill with a solution of one pound of Oxalic Acid or Sodium Bisulfate per five gallons of water. Run the engine at operating temperature one-half to one hour, then drain and flush until water is clear. Fill with a solution of one-half pound of Sal Soda per ten gallons of water and run the engine ten minutes. Drain, flush and fill with water, adding corrosion inhibitor or the desired amount of anti-freeze.

DRAINING: The cooling system is drained by removing the radiator cap, opening the valve in the bottom of the radiator, removing the drain plugs from the water pump and from the left side of the diesel engine block.

FILLING THE COOLING SYSTEM: When filling a cooling system it is essential for the system to be filled completely and air pockets elimi-

Proper filling procedure is necessary to assure the cooling system is completely filled. Follow the four step recommended procedure.

1. Fill the radiator without interrupting the flow of fill water.
2. Start the engine.
3. Complete filling with the engine running at low idle. It is important this filling be completed as quickly as possible after engine start-up.
4. Before installing the radiator cap allow the engine to run at low idle for several minutes then add coolant as necessary. Warm coolant circulating in the top tank is a good indication the system is full. Make sure the system is bled of air and refilled with coolant after a short period of operation. Normally the air will purge out the air vent line leading to the top tank of the radiator.

TESTING THE TEMPERATURE GAUGE: Remember that boiling point temperature and pressure go hand-in-hand and neither one can be tested logically without considering the other. For example, the effect of pressurization and altitude on the boiling point of water is shown in the chart.

If overheating and loss of coolant is a problem, a pressure loss in the system could be the cause. If an overheating condition is indicated on the temperature gauge and loss of coolant is not evident, check the accuracy of the temperature gauge. Make this check by installing a thermometer with a suitable bushing into the cylinder head.


Use CAUTION when working around moving parts with the engine running.

Start the engine. Partially cover the radiator to reduce air flow and cooling. The reading on the instrument panel gauge should agree with the reading on the thermometer.

Testing Cooling System Pressure

The cooling system is designed to work under a pressure of 4-7 PSI (7 PSI is recommended) to allow a high heat transfer for size of radiator and fan combination. In a pressurized system, a leaking radiator cap allows loss of pressure and coolant. For a simple check of cooling system pressure, install a pressure gauge in the radiator top tank and pressurize the system. Do this by either using an air valve and external air supply, hand pump, or by operating the machine until the coolant reaches operating temperature. System pressure should rise to approximately 7 PSI, and any additional pressure should force air past the relief valve through the overflow opening. Do not allow pressure to exceed 10 PSI. The system should hold a minimum pressure of approximately 7 PSI, and pressure must remain constant with the air supply shut off or the engine running at a constant temperature.


If the pressure isn't maintained, overflow loss can occur as cooling system temperature rises. Do not remove the cap while the system is at operating temperature. Check coolant level only when cold.

If the system does not hold pressure, find the leak.

Carefully inspect the radiator cap, seals, sealing surfaces and the top tank filler neck surface for damage.


THERMOSTAT: The opening temperature of the thermostat (bench test in atmospheric pressure) should be approximately 165 ± 1°F (74 ± 1°C). The thermostat should be fully open at approximately 180°F (85°C).

1. Remove the thermostat from the housing.
2. Submerge the thermostat and a thermometer in a pan of water as shown.
3. Apply heat to the pan and stir the water to maintain uniformity.
4. Observe the opening temperature of the thermostat.


If the thermostat does not operate correctly, install a new thermostat.

WATER HOSES: Inspect all water hoses every 10,000 miles and replace if they show signs of cracking or leaking. Periodically replace all radiator and heater hoses, as it is many times difficult to determine the condition of a water hose by visual inspection and feel. Coolant hoses are expendable items and periodic replacement is considered good maintenance practice.

AIR, GASES AND STEAM IN THE SYSTEM: Incomplete or improper filling is a major cause of air in the cooling system. Also, leaks in various components such as the aftercooler, and hoses allow air to enter the cooling system, especially on the inlet side of the water pump.

Air in the system produces foaming or aeration and affects water pump performance. The air bubbles insulate various parts of the engine from the coolant, and hot spots form. As the air bubbles circulate or break up, coolant contacts the hot surfaces, creating steam. The steam pockets have basically the same effect as air bubbles, accelerating the formation of more steam. Consequently, coolant discharges through the overflow.

Exhaust gas leakage into the system causes similar conditions. Exhaust gas can enter through internal cracks or defective cylinder head gaskets.

Most of the causes can be checked by a visual inspection, while others require disassembly or a simple test.

Air in the cooling system is one cause of overheating which can be located by a simple test known as the "bottle test". The equipment required to perform such a test consists of a 1 pint bottle, a bucket of water, and a length of hose with an inside diameter large enough to fit over the end of the radiator overflow pipe.

TO TEST: Fill the cooling system to proper level. Wire open the relief valve in the radiator cap. Install the radiator cap and tighten. Assemble the rubber hose over the end of the overflow pipe.

Start the engine and operate it at high idle speed for at least five minutes after the engine reaches operating temperature. Block off part of the air flow through the radiator to maintain operating temperature. After the temperature has stabilized and all expansion air has vented out, place the loose end of the hose in the water filled bottle which is inverted in the bucket of water. If it takes less than a minute to displace the water in the pint bottle, leakage into the cooling system is excessive.

Loose precombustion chambers, faulty precombustion chamber seals, a loose cylinder head, or a damaged head gasket are possible causes of air in the cooling system. In any case, the cause should be corrected immediately.

WATER PUMP: The water pump circulates the coolant through the aftercooler and oil cooler, the cylinder block, cylinder head, and radiator. Poor coolant circulation causes overheating. A badly corroded or worn water pump impeller, or even a loose impeller, reduces circulation and efficiency.

Every 100,000 miles inspect the water pump and rebuild as necessary, or install a rebuilt pump to reduce down time to a minimum. Your authorized dealer is familiar with worn replacement limits and with disassembly and assembly procedures.

AFTERCOOLER: The aftercooler is a simple device resembling a small radiator core. Water from the engine passes through the core tubes. Engine inlet air, warmed by the turbocharger compressor is directed through the core and around the tubes. Since the temperature of the water is lower than the air, the air is cooled as it leaves the aftercooler and becomes more dense as it enters the intake manifold. This means more air (oxygen) is available for combustion, resulting in more fuel being burned and more power produced.

One degree increase in inlet air temperature increases exhaust temperature approximately three degrees. Restrictions to either coolant or air flow reduce aftercooler efficiency and severely affect the engine and cooling system.

Every 300,000 miles or when engine is being rebuilt, remove the aftercooler and clean core, water and air passages.

FAN BELTS: Every 10,000 miles examine the drive belts for wear and replace if they show signs of wear. Loose or worn pulley grooves cause belt slippage and low fan speed. If fan belts are too loose, they vibrate enough to cause unnecessary wear on the belts and pulleys and possibly slip enough to cause overheating.

If one belt in a set requires replacement, always install a new matched set of belts - never replace just the worn belt. If only the worn belt is replaced, the new belt will carry all the load - as it will not be stretched as much as the older belts - and all the belts will fail in rapid succession.

ADJUSTMENT: Check new belts for adjustment after the first 500 miles and every 10,000 miles thereafter. To check belts - apply 25 lbs. (11,5 kg) force midway between pulleys. Correctly adjusted belts will deflect 1/2 inch (12,5 mm) 3/4 inch (19 mm) for the first check. Maintain later adjustments at 7/8 inch (23 mm).

TO ADJUST: Loosen the alternator belts by loosening the adjusting nuts. Loosen the locknuts on the fan pulley adjusting bracket and adjust fan pulley with the adjusting bolt. After belt tension is correct, tighten locknuts. Readjust alternator belt tension and tighten adjusting nuts. (See page 50.)